1. Field of the Invention
The present invention relates to an ignition system for an internal combustion engine for use in connection between a coil portion body of an ignition coil and a spark plug for the internal combustion engine.
2. Description of the Background Art
Distribution of high voltage to each spark plug by a distributor is disadvantageous in wear of a distributing portion including a distributor cap and a distributor rotor arm and in electrical noises from the distributing portion. To prevent such disadvantages, distributorless ignition systems have been proposed. One of the distributorless ignition systems is designed such that a conductor connecting portion directly connects a coil portion body for generating high voltage and a spark plug to provide the high voltage in the coil portion body to the spark plug, which is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-52175 (1993), Japanese Utility Model Application Laid-Open No. 5-30467 (1993), and Japanese Patent Application Laid-Open No. 5-99112 (1993).
The conductor connecting portion generally comprises a conductive member such as a single spring, a metal round bar and a metal cylinder, and an insulating member for coating the conductive member. There are a variety of processes for positioning the conductive member relative to the insulating member.
For example, the conductive member is forced into the insulating member formed of a flexible rubber such as silicone rubber in a cylindrical shape. In another process, the insulating member comprises a sleeve which is a molded resin component, a rubber-made cap and bushing fitted on opposite ends of the sleeve, and the conductive member is inserted in the sleeve, or the sleeve and conductive member are formed into a unitary structure.
However, the first process might damage the insulating member made of silicone rubber and the like when receiving the conductive member to cause the damaged portion to be thinner, resulting in dielectric breakdown and low reliability. Further, the first process requires a large amount of costly silicone rubber, adding to material costs.
Forming the sleeve and conductive member into a unitary structure in the second process adds to fabrication costs because of the single-piece formation. Inserting the conductive member in the sleeve in the second process involves providing a stepped portion in the sleeve and a stepped portion in the conductive member for engaging the stepped portion of the sleeve for positioning the conductive member in the sleeve. In this case, there is a danger of the conductive member slipping off the sleeve unless the conductive member is coupled to parts of the ignition coil.